Helicopter stabilizing device



Jan. 20, 1953 E. R. DOAK 2,625,997

HELICOPTER STABILIZING DEVICE I Filed Nov. 1, 1946 5 Sheets-Sheet l Jan. 20, 1953 E. R. DOAK HELICOPTER STABILIZING DEVICE 5 Sheets-Sheet 2 Fild Nov. 1, 1946 Jan. 20, 1953 E. R. DOAK HELICOPTER STABILIZING DEVICE Filed Nov. 1; 1946 3 Sheets-:Sheet 3 Zjvwwwtom Patented Jan. 20, 1953 HELICOPTER STABILIZI'NG'DEVICE" Edmond --R. Doak, Los Angeles, iC alif.,.assignor.to

Doak Aircraft Company, ,Inc., Torrance, Calif.', acorporation of California Application November 1, 19.46; Serial N;-1707;1'29- 11 Claims. (Cl. 170 -160,13),

l. Thepresentinvention relates to a method'and apparatusfor stabilizing lifting rotors usefulln helicopters Slight and nonuniform disturbanceson a helicopterrotor resulting from, for example, a .nonuniform air stream, are amplified by the rotating rotor-to cause relatively large unbalanced forces to be exerted thereon. Such unbalanced forces, in turn, cause displacement of the rotor fromits normaliestablished plane of rotation and,-further, such displacement results in a roll and/or pitch of" the rotor.

Such roll or pitch is accompanied :by translation of the rotor in such a manner anddirection that-new forcesact on the rotor opposing: the forces which initially cause the roll and/orpitch; these new forces, however,- are equally'unstable and cause unbalanced forceson the. rotor greater= than the original unbalanced forces. Thus, the resulting disturbances and-unbalanced forces are cumulative in nature and'worsen to the extent that the rotor plane is acceleratedfrom its initial normal plane of rotation intoa relative unstableposition. As a net result'the flight path of the helicopter istranslational and undulates through Wide angles of pitch and/or roll;

Under such circumstances, if the liftingrotor is-constrained' for hovering flight, these unstable forces produce a violent wallowing oscillation which rapidly increases in amplitude until an angle is attained' where the vertical component of'th'e lift forces vector no longer supports the weight of the'h'el-icopter andit falls abruptly.

These facts'of unstability are, in the present stageof the helicopterart, corrected before they becomecatastrophic bythe pilots operation of 'therotor pitch controls which require his continuous and undivided attention.

It is,-therefore, anobject ofthe present invention-to provide a new and improved method and apparatus for stabilizing helicopters characterized by therelief it'gives to the pilot.

Another object ofthe present invention is to provide apparatus automatically operative immediately upon the inception of unbalanced forces ona helicopterrotor for neutralizing such unbalanced? forces in simple, expeditious; manner:

Yet another object of the present invention 'is to provide improved apparatusfor;stabilizing the flight-of a helicopter:

The features of the presentinvention which are believed-to, be novel aresetforth with particularity in the appended, claims. This invention-itself, both-rassto. its organization andyman- 2. ner of operation, together with further, objects and advantages thereof, may be 'best. understood by reference to .theefollowing description. taken iniconnection .withthe accompanying drawings in...which:

Figure 1 shows a helicopterin which ,themethodhand. apparatus. of the. instantsinvention is present.

Figure 2 is-a viewinperspective of. one ,of. the rotor blades; partly, broken away, shownin Figure-l.

Figure 3; isa sectionaliview .taken substantially on ,the l-ine.3.- -3@of. Figure 2...

Figure 4 isa sectionalview taken substantially on the line- 44 ;of,,Fig.ure. 3..

Figure -5 is .asectional view taken substantially on ,the line 5.- 5 of-Figure .6 in which amodified structure. is shown.

Figure-=6 is a...perspectiv e viewof one,.of the rotor .blades,. similar to Figure. 2, andshows a modified-structure.

Figure 7.15 a .view, .partly. structural and, partly diagrammatic,. showing. the. electrical interconnection of the elements showninj'igure. 6.

Figure'8 is an enlarged view .ofsome of vthe. apparatus shown riniFigure, 6.:

Figures isa perspective ,viewofone of the retor blades similarrto Figure. 2,.and showsv another modifiedstructure embodying.- the present inven- 11011.;

Figure 10 .is ,a vview, .partly. in structural and partly, in. diagrammatic. form,..showing .the .manneriin whichelements shownvin Figure-9 are interconnected.

Figure. llisan enlarged view of another modified structure incorporatingthe present invention.

Figures.l2..and 13 v show other modifications of the apparatus embodyingv the. present invention.

In accordance with certain aspectsof the pres- .ent inyention,..the. helicopterrotor stabilizer includes. a small centrifugally operated we ght, preferably. within the confines of. the rotor. and hinged universallywith the. hinged =axes1 parallel to the. rotor plane so thatcentrifugal forces will tmaintainthe. weight in ornearly parallelto the plane of rotation from where. it ..nods and/or precesses. .in..a direction ,normal. to the direction of, the centrifugal. forces .whenand asthe rotor changes .its plane of rotation. Such nodding and/or precessing of theweight causes operation of an aerodynamic element- -such as aspoiler and/or flap-in sucha manner astoincrease or decrease, as the case may be, the blade lift in the azimuth wherethe-liftLie-unbalancedand-is caus- .ing -'the;-rotor; to change its plane of? rotation.

Movement of the centrifugally operated weight may be imparted to the aerodynamic elements such as a spoiler or flap by a simple mechanical linkage or a servo-unit of the electric hydraulic or pneumatic type controlled in accordance with movement of the weight.

In Figure 1 .the helicopter is, of conventional construction and has a rotor ID with three blades II, I2 and I3, which are also of conventional structure and adjustment and are driven in conventional manner. However, each one of the blades has indiv dual lift control means associated therewith in accordance with the present invention. Such lift control means may be an air spoiler or a trailing ed e flap operated b a simple mechanical lifter or electrical, pneumatic or hydraulic servo-mechan sm which in turn is operated upon movement of a centrifugally operated member or yroscopic control member in accordance with the many modifications of the present invention shown and described. herein. These different stabilizing devices are shown in the drawings as associated with the rotor blade I I, but it is understood of course that an identical stabilizer mechanism is present on each one of the other two blades I2 and I3. I

In the particular arrangement shown specifically in Figures 2 to 4, a centrifugally operated weight I4 is affixed on one end of a lever I5, which is pivoted at a point I5 intermediate its end with the other end of the lever I5 formed as an air spoiler I'I, normally confined within the confines of the blade II, but arranged to pass throu h a slotted opening I8 in the up er surface of the blade II (as shown in dotted lines in Figures 3 and 4) upon movement of the weight I4 from its normal position. When the blade I I is rotated in its normal plane of rotation acting on resultant unbalanced forces on the rotor III, the weight I4 is ur ed under centrifu al forces actin thereon to its normal position shown in full lines in Figures 3 and 4 wherein a plane longitudinally through the center of blade I I passes through the geometrical center of the Weight I4.

In the event there is an unbalanced force present on the rotor I II, the rotor as a whole is moved bodily to a skewed position wherein each one of the blades as it rotates is moved upwardly; but when and as a blade moves upwardly the centrifugal force on the weight I4 tends to maintain it in its original pos tion with a result that the air s oiler I1 remains relatively stationary and the blade I I moves relative thereto so as to cause exposure of the spoiler I1 and consequent spoiling of the air stream on the upper surface of the blade. II. This air spoil ng, of course, results in loss of lift in that particular blade and, accordingly, it drops down in a direction approaching the normal position it otherwise occupies when no unbalanced forces are present on the rotor. In its dropping movement the blade I I gradually, in a continuous step, confines more and more the air spoiler I! to produce less and less air spoiling whereby the blade I I gradually returns to its normal position (corresponding to no unbalanced naled on a shaft having its opposite ends anchored respectively in suitable bracket members 2| and 22.

In the modified arrangement shown in Figures 5-8 the lift of the blade II is controlled by positioning a trailing edge flap 25, which is pivotally mounted on a shaft 26 and is movable by means of an electrical servo-mechanism 24 from its normal position shown in full lines in Figure 5 to either one of its two extreme positions shown in dotted lines. The shaft 26 is suitably journaled at the spaced points 21 and 28 (Figure '7) in the blade II with a crank arm 29 affixed to shaft 26 and extending therefrom for engagement with and movement by the longitudinally movable rod 30 extending from the free end of the crank arm 29 into the servo-mechanism 24 for actuation thereby. The servo-mechanism 24 is arranged to move the actuated rod 30 in two directions as indicated by the arrows 3| in Figures 5 and 7 upon selective energization of the solenoid coils 24A and 243. The electrical servo-mechanism 24 is arranged to move the flap 25 down from its normal position when the blade II is skewed up wardly in response to unbalanced forces on the rotor proper; and, conversely, the servo-mechanism 24 moves the flap 25 upwardly from its normal position when the blade II is skewed downwardly in response to unbalanced forces acting on the rotor proper. Hence, during one complete revolution of one of the blades II, I2 or I3, as the case may be, while the rotor proper is skewed because of unbalanced forces acting thereon, the flap 25 is caused to make one oscillation about its normal full line position shown in Figure 5.

The servo-mechanism 24 has four terminals, the input terminals 34A and 34B and the output terminals 35 and 36. When the terminal 351s grounded a current flows from the positive terminal of the voltage source 31 which has its center tap grounded. When the terminal 36 of coil 24A is grounded, current flows through the coil 24A from the negative terminal of the voltage source 31. The terminals 35 and 36 are grounded through one of the pair of switches 38 and 39. The switches 38 and 39 comprise respectively a pair of fixed contact members 42, 44 and 4|, 43 stationarily mounted with respect to the blade II and a corresponding movable contact 46 and 45, each of which is arranged to move respectively in the direction indicated by the arrows 48 and 41 in response to movement of the weight I4. The weight I4, due to the action of centrifugal forces acting thereon, imparts movement to the movable switch contact elements 4!? and 45 in the directions 48 and 4! respectively through the universal connection 50.

The weight I4 is mounted for universal movement on the rotor blade I I, the rod 5| extending axially from the cylindrical weight I4, to which it is afiixed, being fastened to the ring member 52 which is pivotally mounted on the U-shaped bracket 53 on the blade II by means of the cross shaped member 54. Since a gyroscope is defined as a rotating Wheel universally mounted, the weight I 4 since it is mounted for universal movement on the rotor blade II has the same forces applied thereto as a gyroscope. In this connection precession of the weight I4 may be defined as follows: when the weight I4 is subjected to a force which tends to alter the direction of the axis about which it rotates in space, the force meets with great resistance, and the weight I4 will turn about an axis at right angles to the axis about which the force was applied, the movement being such as to place the plane and direction of spinning rotation of the weight coincident with the plane and direction of the force by the shortest path. One of the axes of the cross shaped case in a pneumatic control.

member-54 4s -axially-z-al-igned with the cylindrical rod-member 51 on the one hand: and with: the

cylindrical-switcharm 55 on: the other hand, while the other: axis of: the crossushaped member 54 is in quadrature with theaxis ofth'e member 5 hand extends coaxially with theswitchactuating rod- 56'. 1

It is apparent thattthe switch 38v may be considered to be actuated inresponseto 'nodding of the; weight vM whiletheswitch 39i is actuated inresponseto precessing of the weight L4,-the

structure described being responsive to gyroscopic forces. Whentheweight: ll, which-normally travels: in avhorizontal plane, is subjectedv to a force -which tends to alter the direction of its r0.- tational axis in space,the force. meetsrwith great resistance and the ring-shaped member 52:. will turn-about an axis atright angles'to the axis abou-t which the forcewas applied; the-movement being: such as.:to place :the plane; of spinning: r0.- tation oftheweightzl d icoincident with the plane and direction of the forces :by' theshortest path.

When the weight l4 causes the grounded contact member 46130 :engage contact M, .whichin turn is connected to terminal.35, the. flap moves :downwardly thereby to' cause the blade I i to move downwardly; conversely, when. the grounded contact member46i abuts the contact 42 which-:is connected to terminal .36, .the flap 25 moves upwardly thereby to cause theqblade H to be: deflected upwardly.

In response to. precesing movement of" the weight 14, the contact: 45:. engages either contact 43 or-4|, as=tl1e=case may :be, depending: upon the directionorthewunbalancediiorceactingupon the rotor proper. When the contactabuts contact the terminali35i'is grounded to thereby cause'the-flap 257 tomove downwardly to cause movement-of the blade II downwardly; converse- 1y, when the grounded contact member; 45 engagesrthe contact '4 I; the terminal 36 is grounded to thereby cause the flap. 25.to move upwardly to cause upward movement of-the: blade ll.

While the servo-mechanism .24.- shown. and. described in. connection withlthe modification shownzin Figures. 5-8, inclusive, is of. the electrical solenoid type, theservo-mechanismas shown in the modificationin Figures 9 and 10;.may be of the fluid .type wherein the fiuid may be noncompressible asinthe caseof a hydraulicv control,, or may be of the compressible type such as is ,the It is:understood therefore that the description-of Figures 9 and 10 relate equally well; to both the pneumaticand hydraulic types of: control.

The .flap and gyroscopicgcontrol in ,Figures 5 through 9 are identical "andhaveidentical reference numerals; In the modificationyshown in Figure 10.; however, the weight M causes operation-of, a:.conventional. type of valves 60 andle"! respectively, in response to nodding and: precessingmovement-otthe weight M. These valves control: the how of: fluid to the fluid servo.- mechanism 62' having a'fluid piston .63 arranged to: move. the rod 39.. in directions indicatedgby the-arrow. .31 in;Figure =1,0. Fluid: for moving the piston 163:1'is Obtained==from a fluid supply line-- 64 which supplies fluid" to the fluid reservoir: 65 through-a check valve $6. arranged to pass'fluid onlyin the direction of the arrow .61. Fluid'is transferred to the servo-mechanism .62 from the reservoir 65 through one Ofithe four following paths: (1) From reservoir 65 through piping 68,

throughvalve 60; through check valve 59 arranged-to pass fluid only in thedirection indi- .tc: the; tip. .of .z the .blade as possible.

catedgbyi the .arrowwflll ,i; intonthe wr10,w-nwardtend ofsithei servo-mechanism. 62;: (2), From the res.- ervoir through thepiping 68,, through theivalve 6.0,: through the piping 12, through the check valve-liarranged to pass fluid only in the directiorr. indicated by the arrow M, into the upper endaofthe servo-mechanism 62; (3) From the reservoir 65;. through piping 75, valve 6!, through piping .16, through; check valve 69 into the b0t- .tomend of the servo-mechanismtZ; and,.,(4)

From the-reservoir 65. through the piping 15, through the valve 6i, through the piping 18, through the check valve 13 into the upper end of pthe: servo-mechanism 62.

It? isnoted that the. valves fill. and. BI each comprise-twov valves, one of which is actuated atthe; extreme .ends of movement of the arms 55: and56 in an analogou manner in which the arms1-55i and 56 effect operation of the switches 38 and 39 in Figure 8. Corresponding movements of the weight It in thetwo modifications shown in..Figures 5-10 produce corresponding movements .of the flap 25.

Innthe-modification shown in Figure 11, the air-:spoiler-H :is moved upwardly in the direction of. the-arrow inaaccordance with nodding and precessing movement of the weight It. The spoiler-- l is arranged toibe moved upwardly out of its confined-position within the blade H upon energization ofthe solenoid coil M, the Spoiler i'l being'fprmed on .one end of-the pivoted member: 82; wi-th its free end pivotally mounted, on the movablearmature 83.. The solenoid, coil 81 has negcf.1i satermina s., munded' and its ther t r- -mmal.:com1 cted,to he contact members 43 and M, which-form -sw'itch e1ements with grounded contactelements-Mi and 45 in precisely the same manner as; do the identical numbered contacts described in connection with Figure 8; As a -matter of vfact, the switching structure shown in Figures 8 and 11 are identicalbut for the fact that the-contacts 4| and 42' shown in the modification in Figure 8 are not necessary in the modification shown in Figure 11. Upon nodding and/0r precessing of the weight M,- contacts 44 and-46 and/or contacts 43 and t5 engage as the case may be to cause current to flow through the coil 8!. to thereby, cause movement of the spoiler i1 into itsqair spoiling position.

Intheymodification shown in Figure 12, the trailing edgefiap 25 and air spoiler I! are operated simultaneously upon nodding and/or precessing of. the weight M and combines the teatu-resof= theapparatus, shewn in the modifications in Figures 7 and 11. In Figure 12 the apparatus is identical to that described in connection; with Figure-.7 and identical parts have identical. reference numerals. However, in addition theiapparatus in Figure 12 includes an air spoiler 11 arranged to be moved into air spoiling position upon energization of the solenoidcoil 90, which is connectedin shunt or parallel'to'the coil ZQB. Thus, whenever the coil 24B i energized tocause the blade l l to move downwardly, the spoiler il is simultaneously moved to, air spoiling; positionthereby to; cause a-similar li t; 01706 to-;be-,exerted onthe blade ll so that the operation ;ofthe flap'25 and spoiler ll produces a similar lowering. effect on the blade H.

Although I have shown herein the use of both flaps and air spoilers for achieving certain featuress'of thisinvention, liliis understood that I prefer-to: use-the flap. structure and in such case,;I;prefer tea-.placezthemovable flap as close The flap arrangement is preferred inasmuch as it appears rotatable shaft I rotatable with the flap 25 is geared to the shaft lfll through a pair of gears I02 and IE3 having a one to one ratio. The shaft I0! is linked to thefiap on the second one of a two-bladed arrangement to assure equal and opposite movements of the respective flaps on the two blades. Further, it is apparent that springs either of the compression or tension types may be used to bias the flaps or air spoilers in a predetermined normal position.

It is further evident that the position of the air spoilers or flaps may be made responsive either to the closing of an electrical circuit or to the opening of the electrical circuit. In View of the relatively high speed of rotation of the rotatin blades, it is desirable to actuate the flaps or air spoilers as rapidly as possible upon the occurrence of a disturbance. For this reason, it is preferred to cause actuation of such flaps or spoilers by deenergizing an electrical circuit instead of energizing a circuit. For this reason, it is desirable to use electronic equipment associated with a circuit having energy storing properties and arranged so that the flap or spoiler is maintained in normal position when the full amount of energy is stored within such circuit and arranged to cause movement of such flaps or spoilers upon a change in energy in such circuit. This change in energy may be produced by either opening or closing a switch. For example, the electronic apparatus having the general reference numeral Hll normally energizes the magnet H2 to thereby maintain the flap H3 in its normal position against the action of the tension spring H4. Upon closing of the switch I I5, which may be actuated in any of the manners previously described, the normally charged condenser H6 is discharged to thereby effect a control on the equipment H0 such that the magnet coil H2 becomes deenergized whereupon the tension spring H4 causes the flap H3 to move to an effective position for producing stabilization of the type previously described. The apparatus described in connection with Figure 13 is arranged to cause counterclockwise movement of the flap H3. Apparatus essentially the same as that shown in Figure 13 is associated with the flap H3 to cause clockwise movement of the flap H3 in the event that such correction is called for by the actuation of a switch of the same type as switch I I5.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. In a helicopter stabilizing arrangement for stabilizing the flight of a helicopter, in combination with the lifting rotor blade of the helicopter which is subject to pitching and rolling forces while said blade is rotating about its rotational axis, a weighted member, and means mounting said Weighted member for movement on said blade and normally maintaining said weighted member relatively stationary with respect to said blade regardless of the speed of rotation of said blade so long as said blade continues to rotate in a predetermined plane, a lift control element effective to alter the flow of air past said blade to alter the aerodynamic lift forces developed on said blade, means mounting said lift control element on said blade for relative movement between said lift control element and said blade, and means interconnecting said weighted member to said lift control element, said interconnecting means incorporating means whereby said weighted member is effective to change the position of said lift control element relative to said blade when and as said rotational axis of said blade is abruptly changed in response to such pitching and rolling forces to change the lift forces developed on said blade.

2. The invention set forth in claim 1 characterized in that the lift control element is an air spoiler effective to produce turbulence in the air flow past said blade to thereby spoil such air flow.

3. The invention set forth in claim 1 characterized in that the lift control element is a trailing edge flap.

4. The invention set forth in claim 1 characterized in that the lift control element is both an air spoiler and a trailing edge flap, said air spoiler being effective to produce turbulence in the flow of air past said blade to thereby spoil said air flow.

5. The invention set forth in claim 1 characterized in that the interconnecting means comprises a rigid extension of the weighted member.

6. The invention set forth in claim 1 characterized in that the interconnecting means comprises a joined mechanical linkage operated by the Weighted member.

7. The invention set forth in claim 1 characterized in that the interconnecting means comprises an electrically operated servo-unit controlled by the weighted member.

8. The invention set forth in claim 1 characterized in that the interconnecting means comprises a pneumatically operated servo-unit controlled by the weighted member.

9. In a helicopter stabilizing arrangement for stabilizing the flight of a helicopter, in combination with the lifting rotor blade of the helicopter which is subject to pitching and rolling forces while said blade is rotating about its rotational axis, a centrifugally operated weight movably mounted on and Within the confines of the rotor blade and normally maintained relatively stationary with respect to said blade regardless of the speed of rotation of said blade so long as said blade continues to rotate in a predetermined plane, means pivotally mounting said weight on said blade for movement about an axis extending substantially parallel to said predetermined plane, a lift control element effective to alter the flow of air past said blade to alter the aerodynamic lift forces developed on said blade, means mounting said lift control element on said blade for relative movement between said element and said blade, means interconnecting said weight to said lift control element, said interconnecting means incorporating means whereby said weight is effective to change its position relative to said blade when and as the plane of rotation of said blade is abruptly changed in response to such pitching and rolling forces to change the position of said lift control element to thereby change the lift forces developed on said blade.

10. In a helicopter stabilizing arrangement for stabilizing the flight of a helicopter, in combination with a lifting rotor blade of the helicopter which is subject to pitching and rolling forces, a lift control element effective to alter the flow of air past said blade to alter the aerodynamic lift forces developed on said blade, means mounting said lift control element on said blade for relative movement between said element and said blade, a centrifugally operated weight means movably mounting said weight on said blade for movement between said blade and said weight, and normally maintaining said weight in a fixed position relative to the blade regardless of the speed of rotation of said blade so long as said blade continues to rotate in a predetermined plane, said mounting means including means pivotally mounting said weight about an axis which extends substantially parallel to said predetermined plane whereby said weight may nod when and as the plane of rotation of said blade is abruptly changed, means pivotally mounting said weight about an axis which extends in the longitudinal direction of said blade whereby said weight may precess when and as the plane of rotation of said blade is abruptly changed, and means interconnecting said weight to said lift control element to change the position of said lift control element upon movement of said weight.

11. In a helicopter stabilizing arrangement for stabilizing the flight of a helicopter, in combination with a lifting rotor blade of the helicopter which is subject to pitching and rolling forces,

a weighted member normally maintained sta- 1 10 blade continues to rotate in a predetermined plane, means movably mounting said weighted member on said blade for both pivotal movement of said weighted member about an axis which extends substantially parallel to said predetermined plane, and also for pivotal movement about an axis Which extends generally longitudinally of said blade whereby said weighted member may move when and as the plane of rotation of said blade is abruptly changed in response to such pitching and rolling forces, a lift control element effective to alter the flow of air past said blade to alter the aerodynamic lift forces developed on said blade, said lift control element being effective to alter said flow of air in accordance with the position of said lift control element, and means connected between said weighted member and said lift control element to change the position of said lift control element in accordance with movement of said Weighted member.

EDMOND R. DOAK.

REFERENCES CITED The following references are of record in the file of this patent:

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